The present disclosure relates to an electrophotographic image forming apparatus.
A charging portion of a contact charging system for charging an image carrier has been known in an electrophotographic image forming apparatus. In the charging portion of a contact charging system, a charging roller to which a charging bias voltage is applied rotates while being in contact with the surface of the image carrier, thereby charging the image carrier.
The image forming apparatus may use toner, which includes toner particles and an external additive adhered around the toner particles, for visualizing an electrostatic latent image on the surface of the image carrier. In this case, the external additive having low electric resistance may remain on the surface of the image carrier without being transferred to a transfer target member, such as a sheet material or an intermediate transfer belt.
When the external additive remaining on the image carrier slip through a cleaning portion to move to a charging position of the image carrier and are non-uniformly deposited on the charging roller, image quality is likely to be deteriorated, such as occurrence of density unevenness of an image.
There has also been known that a toner band including the external additive is formed on the image carrier, and a bias voltage is applied to the charging roller, when the region of the toner band on the image carrier faces the charging roller after the transfer of the toner particles to the transfer roller. According to this, the external additive is uniformly deposited onto the surface of the charging roller along the direction of the rotation axis thereof, whereby deterioration in image quality caused by the external additive remaining on the image carrier can be avoided.